The Architecture — How Memory Became a World: The Boot Sequence

In the beginning was the BIOS, and the BIOS counted the RAM, and the RAM was 640K, and it was sufficient.

When power reaches the Intel 8088, the processor does not think. It does not wonder. It begins executing instructions at address FFFF:0000 — the top of the ROM BIOS, the last sixteen bytes of addressable space — because this is what it was built to do, and the 8088 has never had an existential crisis about its purpose. The instruction found there is invariably a JMP, a long jump to the POST routines that live deeper in the BIOS. POST: Power-On Self-Test. The machine counts its own memory, byte by byte, writing and reading patterns like a creature taking inventory of its own body after waking from dreamless sleep. If a byte fails — if the pattern written is not the pattern read back — the machine screams. Not metaphorically. The PC speaker emits a specific sequence of beeps, a Morse code of hardware grief, and halts. A machine that cannot trust its own memory cannot be trusted to do anything at all. This is the first and most honest principle of the 640K: you must know exactly what you ...

From the lore of Conventional Memory.